Brazil’s Civil Defense agency in Rio Grande do Sul updated a storm warning on September 28, accompanied by hail, heavy rain, and strong winds.
In the early morning and morning of September 29, storms were forecast to potentially move north, mainly affecting western and central areas and Missões.
The key point in this warning is not simply whether it will rain, but that rainfall accumulating over a short period and river levels together constitute danger signals.
3-Line Summary
1. A warning for hail and strong winds has been issued for southern Brazil
2. Gusts may exceed 90 km/h
3. Rainfall and river levels are the key concerns
Vigilance for Hail and Strong Winds Through the Morning of September 29
On September 28, Rio Grande do Sul’s Civil Defense agency updated hydrometeorological warning 18/2026 and said that storms were possible across most of the state. The warning included the risk of large hail, heavy rain, and gusts that could exceed 90 km/h.
The Civil Defense agency’s forecast for September 29 said that strong storms could occur in western and central areas and Missões during the early morning and morning, then potentially expand their impact northward in the afternoon. This was a forecast based on weather conditions at the time, not the scale of damage that had already occurred.
From September 28 to 29, cumulative rainfall was forecast to reach 80~120mm in parts of western and central areas and Missões, and to exceed 150mm locally. Rain exceeding 100mm was also expected in the valleys and Serra regions. Heavy rain over a short period is a condition that increases the risk of flooding and flash floods, separately from the wind itself.
Why River-Level Warnings Were Issued as Well
The Civil Defense agency mentioned the risk of flooding along the Ibicuí River, the Santa Maria River, the Jacuí River, the Taquari River, and the Caí River. In these areas, rivers could temporarily exceed their flood-stage thresholds, while flooding of small rivers and streams, urban flooding, and flash floods were also identified as risks.
In particular, the Jacuí, Sinos, and Gravataí rivers in the Guaíba basin were described as already being above flood-alert levels. This means that the rivers of broad low-lying areas are not the only ones requiring caution when additional rain falls. Small rivers and streams where water gathers quickly may also overflow first.
Globo Rural reported that a low-pressure system forming between Uruguay, Rio Grande do Sul, and the Atlantic could lead to the formation of an extratropical cyclone and a cold front, creating storm conditions in the South, Midwest, and Southeast. In Rio Grande do Sul, the possibility of strong winds and hail and rising river levels had to be viewed as a single combined risk.
References
Tags #BrazilWeather #BrazilStorm #RioGrandeDoSul #StrongWinds #Gusts #Hail #HeavyRain #FloodingRisk #RiverFlooding #ExtratropicalCyclone #ColdFront #SouthAmericaWeather